It is customary to utilize a rotatably mounted inking member such as an ink roller in commercially available postage meters. The characters located on the printing die are inked by this roller just prior to printing. This roller is generally supported in brackets of an inking carriage which is mounted for multiple movement in the device. When a mailpiece is inserted into the meter, causing the meter to cycle, the inking roller is moved across the print characters. It is important that the inking be controlled so as not to unintentionally mark portions of the inserted mailpiece. In addition, ink contact with adjacent plastic components of the postage meter could reduce the mechanical properties of these components. Specifics of these types of postage meters are described in U.S. Pat. Nos. 3,244,096 and 4,412,491.
The ink used in postage meters is rather unique and formulated solely for use in postage meters. The ink by itself does not readily dry, but upon contact with paper or other substantially porous receptors it becomes fixed and relatively smudge-proof. The ink has a comparatively long shelf life and its evaporation rate is less than 2% weight loss in two months and less than 10% in 36 months. It has relatively little effect on metallic postage meter components such as those made from magnesium, brass, cadmium, chromium, steel or aluminum. However, because of its chemical components, the ink used in postage meters can have deleterious effects on plastic parts and components of the meter. The basic chemical composition of this type of ink is approximately 50% dioctyl phthalate and about 20% mono and dialkyl benzenes with a fluorescence material also present.
A serious problem encountered when using or changing ink-containing rollers is the contacting of this ink with adjacent plastic components. If the ink contacts a plastic structure having two surfaces in apparent contact, the ink will wick between the surfaces by capillary action and will spread through substantially the entire space between these surfaces. While the phenomenon of capillarity is usually associated with tubes of small diameters, it also occurs between adjacent surfaces having a small space therebetween. As mentioned, this phenomenon is most marked in capillary tubes, that is, tubes of very small diameter. Capillarity depends upon the forces created by surface tension (q.v.) and by wetting of the sides of the tube. In cases in which the forces of adhesion of the liquid to the solid (wetting) exceed the forces of cohesion within the liquid (surface tension), the surface of the liquid will be concave and the liquid will be drawn into the tube--that is, will rise about the hydrostatic level. This action is typified by water in clean glass tubes. In cases where the forces of cohesion exceed the forces of adhesion, the surface of the liquid will be convex, and the liquid will be repelled from the tube--that is, will fall below the hydrostatic level. This action is typified by water in greasy glass (where the adhesion is small) and by mercury in clean glass (where the cohesion is large). Familiar examples of capillary rise are the absorption of water in a sponge, ink in a blotter, or coffee in a lump of sugar, and the rise of kerosene or molten wax in a wick. This same effect occurs when the ink above described is in touch with surfaces in close proximity. Thus, when an operator changes the ink roller in a postage meter, he or she could unintentionally touch the adjacent plastic components with the roller. This causes, in many instances, this unwanted capillary effect on these plastic parts which eventually destroys or reduces their mechanical properties and causes damage to the meter.
Various non-leaking ink systems have been attempted in structures other than postage meters. These solutions, however, do not apply to postage meters in part because of the uniqueness of the ink required in postage meter use. Some of these devices are disclosed in U.S. Pat. Nos. 4,165,688; 4,414,900; 4,437,405 and 4,440,083. There is not known, however, an effective deterent to ink migration or contamination of the type described above relative to postage meters.